The present invention relates to a glaucoma diagnosis apparatus and a recording medium for glaucoma diagnosis suitably used for early glaucoma diagnosis. In the field of medical science, the glaucoma is considered a disease accompanied by the loss of the bundle of fibers of the optic nerve due to a high intra-ocular pressure or the like. For the purpose of glaucoma diagnosis, a color fundus image has conventionally been photographed using the color fundus camera.
The optic nerve fiber layer has a tendency to reflect much more green light (G component of light) and blue light (B component of light). Especially, it reflects the G component of light in a higher proportion than the other component of light. In the case where an image is displayed only with the G or B component, therefore, the brightness of the image of the fundus area (fundus portion) having the loss of the optic nerve fiber layer is lower than the fundus area having the normal optic nerve fiber layer. The fundus image displayed with the G component or the B component is compared with the surrounding areas, and if there is any darker part in the fundus area, the particular part can be diagnosed as an area where the optic nerve fiber layer may be lost. The thicker the optic nerve fiber layer is, the larger amount of the reflected light of the G or B component is obtained. On the other hand, the red light (R component of light) has a tendency to be reflected less by the optic nerve fiber layer than by the fundus tissue which is located much deeper position than the optic nerve fiber layer.
The aforementioned fact will be explained with reference to the thesis entitled xe2x80x9cThe Spectral Reflectance of the Nerve Fiber Layer of the Macaque Retinaxe2x80x9d, pp. 2393-2402, Investigative Ophthalmology and Visual Science, Vol. 30, No. 11, November 1989.
FIG. 7 is a diagram showing a model of a fundus image. In FIG. 7, areas A to C and G are where the optic nerve fiber layer normally exists, and areas D to F are where the optic nerve fiber layer is intentionally removed. These areas A to G are irradiated with light or different wavelengths, respectively, all the light reflected from each one of the areas A to G is received, and the total reflectivity for each area with the wavelength as a parameter is plotted in a graph shown in FIG. 8.
In FIG. 8, the left end indicates the reflectivity of blue light, the right end the reflectivity of red light, and the middle point the reflectivity of green light. As apparent from FIG. 8, the reflectivity of red light is larger than that of the light shorter in wavelength.
The reflectivity of only the optic nerve fiber layer for the areas A, B and C is plotted in the graph of FIG. 9. It is read in FIG. 9 that the reflectivity is gradually reduced as the position moves from area A to area C. This is considered due to the fact that the reflectivity is high at the papilla where the optic nerve fiber are concentrated and having increased thickness, which has increased density of the optic nerve fiber, while the thickness and the density of the optic nerve fiber are reduced with the distance from the papilla. Thus it is read that there is a correlation between the thickness of the optic nerve fiber and the reflectivity.
The progress of glaucoma leads to blindness, and therefore, early detection of glaucoma is of urgent necessity. Since the thickness of the optic nerve fiber layer on the fundus varies from one part to another, the fundus image of even a healthy person photographed and displayed in G and B components develops a gradation and it is difficult to determine at first glance whether an area exists or not where the optic nerve fiber layer is lost.
In view of this, a diagnosis technique has been proposed in which an image processing in which two concentric circles of different radii are plotted around the papilla on the fundus image, and with the first circle as an origin, the image data of the G and B components are integrated (or the finite sum is taken) along the radial direction to the second circle, so that a small change in the amount of reflected light caused by the area where the optic nerve fiber layer is lost is replaced by a large change and displayed as a graph taking advantage of the fact that the optic nerve fiber layer is extended substantially radially from the papilla. Based on this graph it is determined whether there exists an area where the optic nerve fiber layer is lost on the fundus.
The illumination of the fundus, however, develops illumination irregularities at various points, which may cause a gradation with a dark image even in the fundus area having the optic nerve fiber layer. In such a case, it becomes harder to distinguish a fundus area where an optic nerve fiber layer exists from another fundus area where the optic nerve fiber layer is lost. Especially in the initial stage of progress of glaucoma when the optic nerve fiber layer is lost only slightly, illumination irregularities makes it difficult to determine whether a particular patient is going to suffer from glaucoma or not.
Especially, the sign of the chronic loss of optic nerve fiber layer cannot be caught at first glance, and therefore the possibility of the disease cannot be determined.
The present invention has been achieved in view of the situation described above, and the object thereof is to provide a glaucoma diagnosis apparatus capable of substantially overcoming the difficulty of early glaucoma diagnosis caused by the illumination irregularities of the fundus.
According to first aspect of the invention, a glaucoma diagnosis apparatus characterized in that the glaucoma is diagnosed based on reflected light intensity ratio data which are obtained by division calculation such that the image data corresponding to the reflection intensity of the light of short wavelength is divided by the image data corresponding to the reflection intensity of the light of longer wavelength for each part of the fundus image photographed by a color fundus camera is provided.
According to second aspect of the invention, a glaucoma diagnosis apparatus characterized in that the glaucoma is diagnosed based on reflected light intensity ratio data which are obtained by division calculation such that the image data corresponding to the reflection intensity of the light of short wavelength is divided by the image data corresponding to the reflection intensity of the light including longer wavelength for each part of the fundus image photographed by a color fundus camera is provided.
According to third aspect of the invention, a glaucoma diagnosis apparatus characterized in that the glaucoma is diagnosed based on reflected light intensity ratio data which are obtained by division calculation such that G component image data corresponding to the reflection intensity of the G component of light or B component image data corresponding to the reflection intensity of the B component of light is divided by sum of said G component image data, said B component image data and R component image data corresponding to the reflection intensity of the R component of light for each part of the fundus image photographed by a color fundus camera is provided.
According to fourth aspect of the invention, a glaucoma diagnosis apparatus characterized in that the glaucoma is diagnosed based on reflected light intensity ratio data which are obtained by division calculation such that G component image data corresponding to the reflection intensity of the G component of light or B component image data corresponding to the reflection intensity of the B component of light is divided by R component image data corresponding to the reflection intensity of the R component of light for each part of the fundus image photographed by a color fundus camera is provided.
According to fifth aspect of the invention, a glaucoma diagnosis apparatus characterized by comprising arithmetic means for calculating the reflected light intensity ratio data which are obtained by division calculation such that G component image data corresponding to the reflection intensity of the G component of light or B component image data corresponding to the reflection intensity of the B component of light is divided by sum of said G component image data, said B component image data and R component image data corresponding to the reflection intensity of the R component of light for each part of the fundus image photographed by a color fundus camera in order to make a glaucoma diagnosis is provided.
According to sixth aspect of the invention, a glaucoma diagnosis apparatus characterized by comprising arithmetic means for calculating the reflected light intensity ratio data which are obtained by division calculation such that G component image data corresponding to the reflection intensity of the G component of light or B component image data corresponding to the reflection intensity of the B component of light is divided by R component image data corresponding to the reflection intensity of the R component of light for each part of the fundus image photographed by a color fundus camera in order to make a glaucoma diagnosis is provided.
In the glaucoma diagnosis apparatus according to one of the above described aspects, the image data for each part of the fundus is replaced with the reflection intensity ratio (corresponding to the reflectivity ratio) for each part of the fundus and thus the image data is reconstructed, therefore, the adverse effect of illumination irregularities can be obviated.
According to seventh aspect of the invention, a glaucoma diagnosis apparatus characterized by said fundus image photographed by the fundus camera is an image obtained by white light illumination is provided.
With the glaucoma diagnosis apparatus according to the seventh aspect of the invention, the arithmetic process can be simplified.
According to eighth aspect of the invention, a glaucoma diagnosis apparatus characterized by said area of each part of the fundus image corresponds to the area of each pixel of CCD is provided.
With the glaucoma diagnosis apparatus according to the eighth aspect of the invention, the area where the optic nerve fiber layer is lost can be determined in fine detail for each pixel.
According to ninth aspect of the invention, a glaucoma diagnosis apparatus characterized by said glaucoma is diagnosed by an image processing with removing blood tube portion in the fundus image is provided.
With the glaucoma diagnosis apparatus according to the ninth aspect of the invention, the glaucoma can be diagnosed by an image processing with removing the blood tube portion of the fundus image, and therefore the diagnosis can be easily accomplished by displaying the image.
According to tenth aspect of the invention, a glaucoma diagnosis apparatus characterized by said image processing is performed in such a manner that two concentric circles of different radii are plotted along the radial direction about the papilla and the reflected light intensity ratio data are integrated along the radial direction to the second circle with the first circle as an origin is provided.
In the tenth aspect of the invention, a small change in the reflected light amount caused by the area where the optic nerve fiber layer is lost is replaced with a large change by integration and can be displayed as a graph.
According to eleventh aspect of the invention, a recording medium for glaucoma diagnosis wherein a program is recorded for calculating reflected light intensity ratio data which are obtained by division calculation such that G component image data corresponding to the reflection intensity of the G component of light or B component image data corresponding to the reflection intensity of the B component of light is divided by sum of said G component image data, said B component image data and R component image data corresponding to the reflection intensity of the R component of light for each part of the fundus image photographed by a color fundus camera is provided.
According to twelfth aspect of the invention, a recording medium for glaucoma diagnosis wherein a program is recorded for calculating reflected light intensity ratio data which are obtained by division calculation such that G component image data corresponding to the reflection intensity of the G component of light or B component image data corresponding to the reflection intensity of the B component of light is divided by R component image data corresponding to the reflection intensity of the R component of light for each part of the fundus image photographed by a color fundus camera is provided.